请补写出下列名句名篇中的空缺部分。

①顺风而呼，____，而闻者彰。（荀子《劝学》）

②____，以手抚膺坐长叹。（李白《蜀道难》）

③大弦嘈嘈如急雨，____。（白居易《琵琶行》）

④____，春与秋其代序。（屈原《离骚》）

⑤纵一苇之所如，____。（苏轼《赤壁赋》）

⑥____，用之如泥沙？（杜牧《阿房宫赋》）

⑦文章，经国之大业，____。（曹丕《典论》）

⑧操千曲而后晓声，____。（刘勰《文心雕龙》）

    Animals are our friends. We can find different animals here and there. Some animals live in big forests(森林) and some animals live with man.

    Animals can help us a lot. Elephants can do some heavy work for us. And dogs can look after the home. The kids like dogs very much. Cats are women's favorite animals.

We can eat their meat. We can make coats and shoes with their skins(皮). We can get milk from them. So man can’t live without animals.           

三角形ABC中,a=15,b=10,A=${60}^{°}$,则$\cos B=$（　　）